http://www.wolframalpha.com/
Type your problem into the bar, wolfram will do damn near anything you could want done to it.
I'd say get one of these:
Casio FX115ES, like $20 at Target or Best Buy or whatever.
Textbook format display, trig, calc, logs, various scientific constants, matrices, all sorts of goodies.
I love mine, gets great reviews too, basically described as 90% of a TI86 besides the graphing capabilities.